In a data processing device which handles image data, in order to reduce bandwidth and power consumption associated with the transfer of large frames of image data in the system, the image data may be compressed. Transferring frames of image data (or portions thereof) in this compressed format thus reduces the overall system bandwidth consumption and power usage, and furthermore reduces the storage space required for such image data to be held in the system, for example when stored in memory. Whilst frames of image data are typically referenced according to a spatial coordinate system, this may not be the most efficient reference system for compressed data, which may for example be compressed in a block-wise manner, and accordingly in this situation there are then at least two addressing schemes used within the system, namely a spatial coordinate scheme and a block-based coordinate scheme. Where the compressed data is stored using a compression which applies the block-based addressing scheme, access to that compressed data must then be made in terms of the required blocks, rather than the spatial coordinates of the uncompressed image data to which it corresponds.